Apparatus for testing a light emitting device, and a method for testing light emitting devices

ABSTRACT

A text fixture ( 1 ) comprises apparatus ( 4 ) for verifying the color and brightness of light emitted from LEDs ( 5 ) of a printed circuit board ( 3 ). A base ( 6 ) of the fixture ( 1 ) supports the printed circuit board ( 3 ) during testing. A mounting panel ( 14 ) locates ends ( 15 ) of a plurality of optical fibers ( 10 ) adjacent the LEDs ( 5 ) on the printed circuit board ( 3 ), and ends ( 21 ) of ht optical fibers ( 10 ) are terminated in a terminating panel ( 20 ) adjacent an image sensing panel ( 11 ). The image sensing panel ( 11 ) comprises an array of individually addressable light and color sensitive pixels ( 25 ) onto which light from the optical fibers ( 10 ) is incident. An analysing circuit ( 12 ) scans the pixels ( 25 ) for determining the brightness values and the tristimulus values of the incident light, and a control circuit ( 9 ) compares the tristimulus values and brightness values with reference tristimulus and brightness values for verifying the color and brightness of the light emitted by the respective LEDs ( 5 ).

This is a National Stage entry under 35 U.S.C. § 371 of Application No.PCT/IE01/00055 filed Apr. 27, 2001; the above noted prior applicationsare all hereby incorporated by reference.

The present invention relates to apparatus for testing at least onelight emitting device on a panel, for example, one or more lightemitting diodes (LEDs) on a printed circuit board, and in particular,the invention relates to such apparatus for verifying if the colour oflight being emitted by the light emitting device is of the correctcolour. The invention also relates to a method for testing a lightemitting device.

Printed circuit boards, for use in computers, and other electronicassemblies include many LEDs and in general the LEDs are of differentcolour for signifying different operational aspects of the circuits ofprinted circuit board. For example, the LEDs may emit light in the redspectrum, the yellow spectrum, the green spectrum, the blue spectrum,and indeed, any other of the colour spectrums. When testing componentson a printed circuit board, it is also important to verify that the LEDsare operational, and also it is important to be able to verify that theLEDs are emitting light of the correct colour, and of the correctbrightness.

It is common practice to test the functionality of the circuits and thecomponents of a printed circuit board by placing the printed circuitboard in a functional test station which typically, comprises a testfixture, which in general, comprises what is commonly referred to as a“bed of nails”. Test signals are applied to the printed circuit board,and voltages generated across the various components and key parts ofthe circuits are monitored for verifying the operational characteristicsof the components and the circuit. However, in general, visualinspection is required for determining if the LEDs are operational, andif they are emitting light of the correct or desired colour, in otherwords, to establish if the correct LED or LEDs have been assembled ontothe printed circuit board, and if so if they are operational. Suchvisual verification of LEDs is far from error-proof. Firstly, a failedLED may be overlooked by an operator due to operator fatigue.Additionally, an operator can confuse a LED of one colour for that ofanother colour, again as a result of operator fatigue. Additionally,visual inspection tends to be relatively slow since the operationalcharacteristics and colour of the LEDs must be individually inspected,and thus sequentially inspected which tends to be a relatively slow andtime consuming process.

Automatic vision testing systems are available which test for both theoperational characteristics and the colour of LEDs on a printed circuitboard, and indeed, other light sources. Typically, such vision testingsystems rely on a video camera and a frame grabber. The video cameraimages the printed circuit board, and the frame grabber grabs an imageof the printed circuit board when the LEDs are powered up. The image issubsequently processed and interpreted by a computer. However, suchautomatic vision testing systems tend to be relatively expensive,relatively large and unwieldy. Additionally, since the image of theprinted circuit board grabbed from the video camera contains asignificant amount of redundant information relatively sophisticatedalgorithms and relatively large amounts of computer processing power arerequired to extract the relevant data from the image in order to verifythat the LEDs are operational, and are emitting light of the correctcolour.

U.S. Pat. No. 4,808,815 of Langley discloses apparatus for testing ifLEDs on a printed circuit board are operational. The apparatus ofLangley comprises a base on which the printed circuit board is placed. Aplurality of optical fibers are located in a panel above the printedcircuit board with the ends of the respective optical fibers located inclose proximity to the corresponding LEDs the operation of which are tobe tested. The optical fibers at their other end terminate in respectivelight sensors, which in response to light emitted by the respectivecorresponding LEDs and transmitted through the optical fibers to thelight sensors output a signal in the event of light being detected, andno signal in the event of no light being detected. The output signalsfrom the respective light sensors are analysed by analysing circuitryfor verifying the operationality of the respective LEDs. However, thisapparatus of Langley is only suitable for determining if the LEDs areemitting light or not, it does not verify the colour of light beingemitted by the respective LEDs. Additionally, since each optical fibermust terminate in an individual corresponding light sensor where aprinted circuit board contains a large number of LEDs a correspondinglarge number of light sensors are required, thus leading to excessivecost and analysing procedures.

There is therefore a need for apparatus for testing at least one lightemitting device on a panel for determining if the device is emittinglight, and if the light being emitted is of the correct colour. There isalso a need for a method for testing one or more light emitting deviceson a panel for verifying the colour of the light emitted by the deviceswhich overcome the problems of known apparatus and methods.

The present invention is directed towards providing such an apparatusand method.

SUMMARY OF THE INVENTION

According to the invention there is provided apparatus for testing atleast one light emitting device on a panel, the apparatus comprising, alight collecting means for individually collecting light from each ofthe light emitting devices, one light, collecting means being providedfor each light emitting device to be tested, and an analysing means foranalysing light from the respective light collecting means, wherein averifying means is provided for verifying if each light emitting deviceis emitting light of the correct colour.

In one embodiment of the invention the analysing means comprises a meansfor determining the tristimulus value of the light collected from eachlight emitting device for facilitating verification of the light colourby the verifying means.

Preferably, a storing means for storing reference tristimulus values forthe respective light emitting devices is provided, and the verifyingmeans comprises a comparing means for comparing the determinedtristimulus values of each light emitting device with the correspondingreference tristimulus value.

In another embodiment of the invention the analysing means comprises ameans for determining the brightness value of the light collected fromeach light emitting diode for facilitating verification of thebrightness of the light by the verifying means.

Preferably, a storing means for storing reference brightness values forthe respective light emitting diodes is provided and the verifying meanscomprises a comparing means for comparing the determined brightnessvalues of the respective light emitting devices with the correspondingreference brightness values.

Advantageously, the analysing means comprises an image sensing panelcomprising a plurality of pixels arranged in a matrix of rows andcolumns, and the respective collecting means direct collected light ontothe image sensing panel at respective spaced apart locations so that thecollected light from the respective light emitting devices is incidenton corresponding pixels of the image sensing panel. Preferably, therespective pixels of the image sensing panel are individuallyaddressable.

In another embodiment of the invention a reading means is provided forreading signals outputted by the respective pixels and for relaying theread signals to the means for determining the tristimulus value andbrightness value of the light from each light emitting device.Preferably, the means for determining the tristimulus value and thebrightness of the light emitted by each light emitting device averagesthe signal values read from respective pixels of groups of pixels inrespective areas adjacent where light from the respective light emittingdevices is incident on the image sensing panel.

In one embodiment of the invention a terminating means is provided forterminating the respective collecting means adjacent the image sensingpanel. Preferably, the terminating means comprises a terminating panelhaving a plurality of locating means for locating the respectivecollecting means at spaced apart locations in the terminating panel.Advantageously, the locating means are arranged in a row in theterminating panel. Preferably, each locating means comprises a locatingbore extending through the terminating means. Ideally, the terminatingmeans extends parallel to the image sensing panel.

In another embodiment of the invention a mounting means is provided formounting each collecting means adjacent the panel to be tested with therespective collecting means being located in close proximity to thecorresponding light emitting devices.

Preferably, the mounting means comprises a plurality of positioningmeans for positioning the respective collecting means in close proximityto the corresponding light emitting devices. Advantageously, eachpositioning means comprises a positioning bore extending through themounting means for positioning the collecting means in close proximityto the corresponding light emitting device. Ideally, the mounting meanscomprises a mounting panel.

In a further embodiment of the invention each collecting means comprisesan optical fiber for extending between the corresponding light emittingdevice and the analysing means.

In one embodiment of the invention the mounting means mounts eachoptical fiber with a corresponding end of the optical fiber spaced apartfrom the corresponding light emitting device a distance from the lightemitting device not greater than 2 mm.

Preferably, the mounting means mounts each optical fiber with itscorresponding end spaced apart from the corresponding light emittingdevice a distance from the corresponding light emitting device lyingwithin the range of 0.5 mm to 2 mm. Advantageously, each optical fiberextends through the corresponding positioning bore in the mounting meansand terminates adjacent a corresponding end of the corresponding bore.

In another embodiment of the invention the terminating means mounts theoptical fibers with their respective corresponding ends adjacent theimage sensing panel but spaced apart from the image sensing panel adistance not greater than 2 mm, and preferably, a distance ofapproximately 0.5 mm.

Alternatively, a focusing lens is located between the terminating meansand the image sensing panel for focusing light from the respectiveoptical fibers on the image sensing panel.

In one embodiment of the invention the apparatus is adapted forverifying the colour of light emitted from a light emitting diode, andpreferably, for verifying the brightness of light emitted by the lightemitting diode.

In another embodiment of the invention the apparatus is adapted fortesting light emitting diodes mounted in a printed circuit board panel.

In a further embodiment of the invention the apparatus is adapted formounting in a test fixture.

In a still further embodiment of the invention the apparatus is adaptedfor mounting in a test fixture for testing parameters of components andparts of circuits of a printed circuit board.

In one embodiment of the invention at least the mounting means isadapted for mounting in a test fixture.

In another embodiment of the invention the mounting means is adapted formounting adjacent a panel of a housing of apparatus to be tested inwhich the light emitting devices are located on the panel, thepositioning means of the mounting means positioning the respectivecollecting means adjacent to the respective light emitting devices onthe panel of the apparatus to be tested.

In a further embodiment of the invention the apparatus further comprisesa control means for controlling a supply of power to the LEDs.

Further, the invention provides a test fixture for testing electroniccomponents connected to a printed circuit board, the test fixturecomprising the apparatus according to the invention.

In one embodiment of the invention the mounting means of the apparatusis mounted in the test fixture so that the mounting means can be urgedtowards the printed circuit board for bringing the corresponding ends ofthe corresponding optical fibers into close proximity with thecorresponding light emitting devices to be tested.

In another embodiment of the invention the test fixture comprises a jigcarrying a bed of nails.

Additionally, the invention provides a method for testing a lightemitting device on a panel for determining if the light being emittedfrom the light emitting device is of the correct colour, the methodcomprising the steps of placing the panel with the at least one lightemitting device in the apparatus according to the invention poweringeach light emitting device on the panel, analysing the light collectedby each collecting means from the corresponding light emitting device,and verifying if the light received from the collecting means from thecorresponding light emitting device is of the correct colour.

In one embodiment of the invention the method further comprisesdetermining the tristimulus values of the light received from therespective light emitting devices and comparing the determinedtristimulus values with corresponding reference tristimulus values forverifying if the light emitted from the respective light emittingdevices is of the correct colour.

In another embodiment of the invention the method further comprisesverifying if the light received from the respective collecting meansfrom the corresponding light emitting device is of the correctbrightness.

In a further embodiment of the invention the method further comprisesdetermining the brightness values of the light received from therespective light emitting devices and comparing the determinedbrightness values with corresponding reference brightness values forverifying if the light emitted from the respective light emittingdevices is of the correct brightness.

The advantages of the invention are many. A particularly importantadvantage of the apparatus according to the invention is that itprovides a relatively simple and inexpensive apparatus for testing lightemitting devices on a panel, for example, LEDs on a printed circuitboard, and as well as providing a test for verifying if the lightemitting devices are emitting light, the apparatus according to theinvention also verifies if the light being emitted by the light emittingdevices is of the correct colour and brightness. Additionally, theapparatus according to the invention is particularly suitable forretrofitting into a test fixture, of the type comprising a “bed ofnails”. A further advantage of the invention is achieved when light fromthe light emitting devices is relayed to the image sensing panel throughoptical fibers, in that the need for lenses and other light focusingdevices is avoided, or in cases where it is desired to focus light fromthe optical fibers onto the image sensing panel, only one lens isrequired. Furthermore, by virtue of the fact that the light from eachlight emitting device is directed onto an image sensing panel the needfor a plurality of individual light sensors at the end of eachcollecting means is avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood from the followingdescription of some preferred embodiments thereof which are given by wayof example only with reference to the accompanying drawings, in which:

FIG. 1 is a schematic front elevational view of a test fixture accordingto the invention for testing a printed circuit board, which incorporatesapparatus also according to the invention for testing LEDs on a printedcircuit board,

FIG. 2 is a perspective view of a part of the apparatus of FIG. 1,

FIG. 3 is a block representation of circuitry of the apparatus of FIG.2,

FIG. 4 is a schematic plan view of the test fixture of FIG. 1,

FIG. 5 is a partly cut away schematic front elevational view of a testfixture according to another embodiment of the invention,

FIG. 6 is a transverse cross-sectional front elevational view of aportion of apparatus of the test fixture of FIG. 5, and

FIG. 7 is a schematic front elevational view of a test fixture accordingto a still further embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings and initially to FIGS. 1 to 4 there isillustrated a test fixture according to the invention indicatedgenerally by the reference numeral 1 for testing printed circuit boards3. The test fixture 1 comprises apparatus also according to theinvention which is indicated generally by the reference numeral 4 fortesting LEDs 5 of the printed circuit boards 3, and for verifying if theLEDs 5 are emitting light and if the emitted light from the respectiveLEDs 5 is of the correct colour and brightness. The test fixture 1comprises a base 6 for sequentially receiving the printed circuit boards3. Locating pins (not shown) are provided extending upwardly from thebase 6 for engaging corresponding bores (not shown) in the printedcircuit boards 3 for locating and aligning the printed circuit board 3on the base 6. Guide pins (also not shown) extending upwardly from thebase 6 slideably engage corresponding bushed bores (also not shown) in amounting frame 7 for guiding and aligning the mounting frame 7 with thebase 6, and in turn with a printed circuit board 3 mounted on the base6. The mounting frame 7 is moveable upwardly and downwardly in thedirections of the arrows A and B, respectively, relative to the base 6between a lower test position adjacent the base 6 and a raised positionspaced apart from the base 6, for facilitating placing and removal ofprinted circuit boards 3 on the base 6.

A carrier plate (not shown) is located in the base 6 and carries aplurality of electrically conductive pins (also not shown) for engagingcorresponding electrically conductive parts of the tracks and/orcomponents of the printed circuit board 3 for carrying out tests of thecomponents and/or circuits of the printed circuit board 3. Such acombination of a carrier plate and a plurality of electricallyconductive contact pins will be well known to those skilled in the art,and typically is referred to as “a bed of nails”. The carrier plate (notshown) is moveable upwardly in the base 6 for engaging correspondingelectrically conductive points of the tracks on the underside of theprinted circuit board 3 with the electrically conductive pins (notshown).

A control means, namely, a control circuit 9 operating under the controlof a microcontroller 8 controls the operation of the test fixture 1. Thecontrol circuit 9 also under the control of the microcontroller 8applies appropriate test signals to appropriate pins of the electricallyconductive pins of the “bed of nails” in the base 6 for carrying outtests on the components and circuits, as well as for powering the LEDs 5of the printed circuit board 3. The microcontroller 8 reads signals fromappropriate pins of the electrically conductive pins of the “bed ofnails” for determining if the components and/or circuits of the printedcircuit board 3 are within desired specifications.

The construction of such test fixtures and their operation will be wellknown to those skilled in the art, and it is not intended to describethe test fixture 1 in further detail.

Turning now to the apparatus 4 for testing the LEDs 5, the apparatus 4comprises a plurality of collecting means provided by respective opticalfibers 10 for collecting light from the corresponding LEDs 5, oneoptical fiber 10 being associated with each LED 5. The optical fibers 10relay light from the corresponding LEDs 5 to an image sensing panel 11of an analysing means, namely, analysing circuit 12, both of which willbe described in more detail below.

A mounting means, namely, a mounting panel 14 located within themounting frame 7 positions ends 15 of the optical fibers 10 at positionsin close proximity to the LEDs 5 when the mounting frame 7 is in thetest position. The mounting panel 14 is moveable upwardly and downwardlyin the direction of the arrows A and B with the mounting frame 7. Aplurality of positioning means, namely, positioning bores 18 extendingthrough the mounting panel 14 tightly engage and position the opticalfibers 10 at positions with the ends 15 of the optical fibers 10 alignedwith the corresponding LEDs 5. Each optical fiber 10 extends through thecorresponding positioning bore 18 and terminates at its end 15 adjacenta lower major surface 19 of the mounting panel 14, so that when themounting frame 7 is in the test position the ends 15 of the opticalfibers 10 are spaced apart from the LEDs 5 a distance “s” which lies inthe range 0.5 mm to 2 mm.

A terminating means, namely, a terminating panel 20 terminates the otherends 21 of the optical fibers 10 adjacent the image sensing panel 11. Aplurality of locating means, namely, spaced apart locating bores 22extend through the terminating panel 19 and are arranged in a row forlocating the ends 21 of the optical fibers 10 in a corresponding rowadjacent the image sensing panel 11. The optical fibers 10 extendthrough the locating bores 22 and terminate at a major surface 24 whichfaces the image sensing panel 11.

The image sensing panel 11 comprises an array of light and coloursensitive pixels 25 which are individually addressable and are arrangedin a matrix of rows and columns for receiving incident light from theends 21 of the optical fibers 10. Some of the pixels 25 are sensitive tored light, some are sensitive to green light and some are sensitive bluelight, and the pixels 25 are arranged in a Bayer pattern. In thisembodiment of the invention the image sensing panel 11 is a PhotobitPB100 supplied by Photobit Corp. of the U.S. Alternatively, the imagesensing panel 11 may be a Sony ILX524 sensor panel. The terminatingpanel 20 spaces the ends 21 of the optical fibers 10 from the imagesensing panel 11 a distance of approximately 0.5 mm. The fact that theends 21 of the optical fibers 10 are slightly spaced apart from theimage sensing panel 11 causes light from each LED 5 to be incident on anumber of corresponding adjacent pixels 25, namely, a group of pixels 25of the image sensing panel 11. However, the spacing between therespective ends 21 of the optical fibers 10 in the locating bores 22 issufficient to avoid light from one optical fiber 10 overlapping withpixels 25 of groups corresponding to adjacent optical fibers 10.

Referring in particular to FIG. 3, the analysing circuit 12 comprises amicroprocessor 27 which under the control of suitable software in a ROM28 scans and reads pixel values from the pixels 25 into a buffer memory29 when the LEDs 5 are powered by appropriate signals applied by themicrocontroller 8 to the printed circuit board 3 through the “bed ofnails”. The microprocessor 27 averages the pixel values of each group ofpixels 25 corresponding to the respective optical fibers 10, andcomputes the brightness and tristimulus values of each LED 5 from theaverage pixel values of the respective groups of pixels 25. Themicrocontroller 8 of the control circuit 9 reads the brightness andtristimulus values from the microprocessor 27 through a parallel port 30or a serial port 31. A comparing means which is implemented in themicrocontroller 8 by suitable software compares the read brightness andtristimulus values of the LEDs 5 with reference brightness andtristimulus values for the corresponding LEDs 5, and determines if theLEDs 5 are operating at the correct brightness and are of the correctcolour. A visual display unit 32 displays the brightness and tristimulusvalues of the respective LEDs 5, and also displays appropriate values ofthe other components and circuits of the printed circuit board 3 whichare determined by the microcontroller 8 from signals read from theappropriate pins of the “bed of nails”. The visual display unit 32 alsodisplays the status of the printed circuit board 3, whether it haspassed or failed the test.

An appropriate operating mechanism for raising and lowering the mountingframe 7 in the direction of the arrows A and B relative to the base 6 isprovided but not illustrated, as is an appropriate operating mechanismfor raising and lowering the carrier plate (not shown) in the base 6 forengaging and disengaging the “bed of nails” with the printed circuitboard 3. Such operating mechanisms will be well known to those skilledin the art.

The terminating ends 15 and 21 of the optical fibers 10 are cut at rightangles to the fiber axis and polished smooth so as to efficientlycollect and output light. The core diameter of the optical fibers 10 canrange between 0.25 mm to 3 mm. While the optical fibers of larger corediameter collect more light optical fibers of diameter greater than 3 mmtend to be bulky and difficult to route around tight corners. Whileoptical fibers in the range of 0.25 mm to 3 mm are of smaller diameterand collect less light they are relatively easy to handle particularlywhere a printed circuit board is provided with a large number of LEDs tobe tested. Tests have indicated that optical fibers of core diameter inthe range of 0.5 mm to 1 mm provide an optimum trade off betweenmanageability of the optical fibers and the light collecting capacity ofthe optical fibers. In order to ensure accuracy the optical fibers 10are secured in the bores 18 and 22 by an epoxy adhesive, and the opticalfibers 10 are a relatively tight fit in the bores 18 and 22 in themounting panel 14 and the terminating panel 20, respectively. Bymaintaining the ends 15 of the optical fibers 10 adjacent the LEDs 5within 0.5 mm to 2 mm light is efficiently collected from the LEDs 5without the risk of damage to the optical fibers 10 from the LEDs 5.

In use, the printed circuit board 3 to be tested is engaged on the base6, and the mounting frame 7 is lowered in the direction of the arrow Bfor urging the mounting panel 14 into the test position with the ends 15of the optical fibers 10 located to receive light from the correspondingLEDs 5. The carrier plate (not shown) in the base 6 is urged upwardlyfor engaging the printed circuit board 3 with the pins of the “bed ofnails”. Appropriate signals are applied to the printed circuit board 6by the control circuit 9 through the pins of the “bed of nails”. On theLEDs 5 being powered the pixels 25 of the image sensing panel 11 arescanned and the pixel values are read into the buffer memory 29. Themicroprocessor 27 averages the pixel values of each group of pixels 25which correspond to the respective fibers 10, and computes thebrightness and tristimulus values of the respective LEDs 5. Themicrocontroller 8 in the control circuit 9 reads the brightness andtristimulus values from the microprocessor 27 of the respective LEDs 5and by comparing the respective values with reference brightness andtristimulus values for the respective LEDs 5 the microcontroller 8determines if the LEDs 5 are operating at the correct brightness valueand are of the correct colour. The status of each of the LEDs 5 isdisplayed on the visual display unit 32. Simultaneously or sequentiallywith the testing of the LEDs 5 the microcontroller 8 also reads signalsfrom the components and circuits of the printed circuit board 3 fordetermining if the components and the circuits of the printed circuitboard 3 are within desired specifications. The results of these testsare also displayed on the visual display unit 32 as is the pass or failstatus of the printed circuit board 3.

Referring now to FIGS. 5 and 6 there is illustrated a test fixtureaccording to another embodiment of the invention indicated generally bythe reference numeral 40. The test fixture 40 is substantially similarto the test fixture 1 and similar components are identified by the samereference numerals. In this embodiment of the invention the controlcircuit and the microcontroller for controlling the operation of thetest fixture 40 and for applying test signals to the printed circuitboard 3 are housed in a housing 41 of the base 6, and are notillustrated. The visual display unit 32 is provided on the housing 41.Additionally, in this embodiment of the invention the carrier platewhich is indicated by the reference numeral 42 and the electricallyconductive contact pins 43 which form the “bed of nails” are illustratedwithin the housing 41. A carrier member 45 within the housing 41supports the carrier plate 42 and is urged upwardly and downwardly forby an pneumatic ram (not shown) for bringing the contact pins 43 intoand out of engagement with the printed circuit board 3. A pluralitypressure members 46 extend downwardly from the mounting frame 7 forengaging the printed circuit board 3 when the mounting frame 7 is in thetest position for urging the printed circuit board 3 downwardly onto aprinted circuit board receiving platform 48 and for in turn supportingthe printed circuit board 3 against the upward force of the contact pins43 for ensuring good electrical contact between the contact pins 43 andthe appropriate electrically conductive tracks of the printed circuitboard 3 to which the test signals are to be applied and read back fromthe printed circuit board 3. An operating mechanism for urging themounting frame 7 in the direction of the arrows A and B between the testand release position is also provided but not illustrated. Locating pinsand guide pins, neither of which are illustrated are provided forlocating the printed circuit board on the platform 48 and for aligningthe mounting frame 7 with the base 6.

Turning now to the analysing circuit 12, the analysing circuit 12comprises a printed circuit board 49 on which the microprocessor 27, theROM 28, the buffer memory 29 and the parallel and serial ports 30 and 31are mounted. Additionally, the image sensing panel 11 is also mounted onthe printed circuit board 49. However, in this embodiment of theinvention the image sensing panel 11 is circular in plan view.Additionally. in this embodiment of the invention the terminating panel20 is mounted on a lens accommodating housing 50. The lens accommodatinghousing 50 is of tubular construction and is of circular transversecross-sectional area, and accommodates a lens 51 for focusing light fromthe optical fibers 10 onto corresponding groups of pixels 25 of theimage sensing panel 11. The lens 51 is a double convex lens with anappropriate diameter and focal length. In practice, it is envisaged thatthe diameter of the lens may lie in the range 5 mm to 25 mm, and thefocal length may lie in the range 4 mm to 30 mm. However, in thisembodiment of the invention the lens is approximately 12 mm in diameterwith a focal length of 5 mm. Screws 52 secure the lens accommodatinghousing 50 to the printed circuit board 49 while screws 53 secure theterminating panel 20 to the lens accommodating housing 50.

It has been found that by focusing the light from the optical fibers 10onto the image sensing panel 11 through the lens 51 a sharper image ofthe light from each optical fiber 10 is focussed on the image sensingpanel 11, and thus the danger of light from one optical fiberoverlapping with pixels of groups corresponding to other optical fibersdoes not arise. Additionally, by focusing the light from the opticalfibers through the lens 51 the number of pixels onto which the light isfocussed is reduced, thus reducing the processing time required fordetermining the brightness and tristimulus values of the respective LEDsand also leading to more accurate values.

Otherwise, the test fixture 40 is similar to the test fixture 1 and itsoperation is likewise similar.

Referring now to FIG. 7 there is illustrated a test fixture according toanother embodiment of the invention, which in this case is provided by atest jig indicated generally by the reference numeral 60. The test jig60 is dedicated to testing LEDs 5 only, which in this case are locatedin a panel 61 of apparatus to be tested, namely, a personal computer 62.Parts of the test jig 60 are substantially similar to correspondingparts of the test fixture 1 and the apparatus 4 described with referenceto FIGS. 1 to 4, and where such parts are similar, similar componentsare identified by the same reference numerals. The test jig 60 comprisesa support jig 63 within which the mounting panel 14 is located. Thesupport jig 63 is adapted for receiving and positioning the personalcomputer 62 relative to the mounting panel 14 so that the ends 15 of theoptical fibers 10 are appropriately positioned relative to the LEDs 5.In this embodiment of the invention there is no need for the mountingpanel 14 or the support jig 63 to be moveable relative to each other,since the personal computer 62 to be tested can be slid into and out ofthe support jig 63 beneath the mounting panel 14, and the mounting panel14 is located in the support jig 63 so that when the personal computer62 is located in the support jig 63 the LEDs 5 are correctly positionedrelative to the ends 15 of the optical fibers 10.

In this embodiment of the invention the analysing circuit 12 is similarto the analysing circuit 12 of the test fixture 40, and similarcomponents are identified by the same reference numerals. The testfixture 60 is controlled by a controlling means, namely, a controllingpersonal computer 65 which powers the personal computer 62 through aconnecting cable 66 for in turn powering the LEDs 5. A keyboard 68 and avisual display screen 69 of the controlling personal computer 65 arealso provided. The analysing circuit 12 is operated under the control ofthe controlling computer 65 to read the pixel values of the pixels 25 ofthe image sensing panel 11 and for averaging the pixel values of therespective groups of pixels 25 and for determining the brightness valuesand the tristimulus values of the respective light emitting diodes 5.Communication between the controlling personal computer 65 and theanalysing circuit 12 is carried out through an interface cable 67through one of the parallel and/or serial ports 30 and 31, respectively.The controlling personal computer 65 compares the brightness values andtristimulus values of the respective LEDs 5 with respectivecorresponding reference values for determining if the LEDs 5 areoperating at the appropriate brightness and are of the correct colour.

Results of the tests are displayed on a visual display screen 69 of thelaptop computer 68.

In use, the controlling personal computer 65 powers the personalcomputer 62 and in turn the LEDs 5. The microprocessor 27 of theanalysing circuit 12 reads the pixel values of the pixels 25 of theimage sensing panel 11 into the buffer memory 29, and subsequentlyaverages the pixel values of the pixels of the respective groups ofpixels corresponding to the optical cables 10. The microprocessor 27then computes the respective brightness values and tristimulus values ofthe respective LEDs 5 from the averaged values from the correspondinggroups of pixels 25. The controlling personal computer 65 reads thecomputed brightness and tristimulus values of the respective LEDs 5 andcompares them with corresponding reference value for passing of failingthe respective LEDs 5 and in turn the personal computer 62. The resultsof the test are displayed on the visual display screen 69.

While the test fixtures described with reference to FIGS. 1 to 4, and 5and 6 have been described for testing the circuits and other componentsof printed circuit boards, it will be readily appreciated that in manycases the test fixture may be provided for testing the LEDs only of aprinted circuit board as in the case of the test fixture described withreference to FIG. 7.

It is also envisaged that while the test fixtures according to theinvention have been described as having the test signals applied to theprinted circuit boards through the “bed of nails” it is envisaged thatin certain cases a socket may be provided into which the printed circuitboard would be plugged for powering thereof, and/or for applying thetest signals therethrough.

Additionally, it is envisaged that where a printed circuit boardcomprises a large number of LEDs to be tested, the locating bores in theterminating panel may be arranged in a matrix comprising a plurality ofrows and columns of locating bores, and the optical fibers wouldterminate in the locating bores, one optical fiber being located in eachlocating bore.

While in the embodiment of the invention described with reference toFIGS. 5 and 6 the test fixture has been described as comprising acarrier member for supporting the carrier plate with the “bed of nails”,and the carrier member has been described as being moveable upwardly anddownwardly by a pneumatic ram for bringing the contact pins of the “bedof nails” into and out of engagement with the printed circuit board, itis envisaged that in a more practical implementation of the test fixturea platform would be provided for supporting the printed circuit board,and the platform would have a plurality of bores extending therethroughfor accommodating the contact pins of the “bed of nails”. The platformwould then be arranged to be drawn downwardly by the application of avacuum so that the contact pins of the “bed of nails” would projectupwardly through the bores extending through the platform for engagingthe electrically conductive tracks on the printed circuit board. Sucharrangements in such test fixtures will be well known to those skilledin the art.

1. Apparatus for testing a plurality of light emitting devices (5) on apanel (3), the apparatus (4) comprising: a plurality of light collectingmeans (10), one light collecting means (10) being provided for eachlight emitting device (5) for collecting light from the correspondinglight emitting device (5), an analyzing means (12) for analyzing lightfrom the respective light collecting means (10), and a verifying means(8, 27, 65) for verifying that each light emitting device (5) isemitting light of the correct color, wherein the analyzing means (12)comprises an image sensing panel (11) comprising a plurality of pixels(25) arranged in a matrix of rows and columns, and the respectivecollecting means (10) direct collected light onto the image sensingpanel (11) at respective spaced apart locations so that the collectedlight from the respective light emitting devices (5) is incident oncorresponding pixels (25) of the image sensing panel (11).
 2. Apparatusas claimed in claim 1 wherein the respective pixels (25) of the imagesensing panel (11) are individually addressable.
 3. Apparatus as claimedin claim 1 wherein the means (12) comprises a means (27) for determiningthe tristimulus value of the light collected from each light emittingdevice (5) for facilitating verification of the light color by theverifying means (8, 27, 65).
 4. Apparatus as claimed in claim 3 in whicha storing means for storing reference tristimulus values for therespective light emitting devices is provided, and the verifying meanscomprises a comparing means for comparing the determined tristimulusvalues of the respective light emitting devices with the correspondingreference tristimulus values.
 5. Apparatus as claimed in claim 3 whereinthe analyzing means (12) comprises a means (27) for determining thebrightness value of the light collected from each light emitting diode(5) for facilitating verification of the brightness of the light by theverifying means (27).
 6. Apparatus as claimed in claim 5 wherein areading means (27) is provided for reading signals outputted by therespective pixels (25) and for relaying the read signals to the means(27) for determining the tristimulus value and the brightness value ofthe light from each light emitting device (5).
 7. Apparatus as claimedin claim 6 in which the means for determining the tristimulus value andthe brightness value of the light emitted by each light emitting deviceaverages the signal values read from respective pixels of groups ofpixels in respective areas adjacent where light from the respectivelight emitting devices is incident on the image sensing panel. 8.Apparatus as claimed in claim 5 in which a storing means for storingreference brightness values for the respective light emitting diodes isprovided, and the verifying means comprises a comparing means forcomparing the determined brightness values of the respective lightemitting devices with the corresponding reference brightness values. 9.Apparatus as claimed in claim 1 wherein a terminating means (20) isprovided for terminating the respective collecting means (10) adjacentthe image sensing panel (11), the terminating means (20) comprising aplurality of locating means (22) for locating the respective collectingmeans (10) at spaced apart locations in the terminating means (20). 10.Apparatus as claimed in claim 9 wherein the locating means (22) arearranged in a row in the terminating panel (20).
 11. Apparatus asclaimed in claim 9 wherein each locating means (22) comprises a locatingbore (22) extending through the terminating means (20).
 12. Apparatus asclaimed in claim 9 wherein the terminating means (20) extends parallelto the image sensing panel (11).
 13. Apparatus as claimed in claim 1wherein a mounting means (14) is provided for mounting each collectingmeans (10) adjacent the panel (3) to be tested, the mounting means (14)comprising a plurality of positioning means (18) for positioning therespective collecting means (10) in close proximity to the correspondinglight emitting devices (5).
 14. Apparatus as claimed in claim 13 whereineach collecting means (10) comprises an optical fiber (10) for extendingbetween the corresponding light emitting device (5) and the analyzingmeans (12), the mounting means (14) mounting each optical fiber (10)with a corresponding end (15) of the optical fiber (10) spaced apart notmore than 2 mm from the corresponding light emitting device (5). 15.Apparatus as claimed in claim 14 wherein a focusing lens (51) is locatedbetween the terminating means (20) and the image sensing panel (11) forfocusing light from the respective optical fibers (10) on the imagesensing panel (11).
 16. Apparatus as claimed in claim 14 in which theterminating means mounts the optical fibers with their respectivecorresponding ends adjacent the image sensing panel, but spaced apartfrom the image sensing panel a distance not greater than 2 mm. 17.Apparatus as claimed in claim 1 wherein the apparatus (4) is adapted forverifying the color, and the brightness of light emitted from a lightemitting diode (5).
 18. Apparatus as claimed in claim 1 wherein theapparatus (4) is adapted for testing light emitting diodes (5) mountedon a printed circuit board panel (3).
 19. Apparatus as claimed in claim1 wherein the apparatus (4) is adapted for mounting in a test fixture(1).
 20. Apparatus as claimed in claim 1 wherein the mounting means (4)is adapted for mounting in a test fixture (1) for testing parameters ofcomponents and parts of circuits of a printed circuit board (3). 21.Apparatus as claimed in claim 1 wherein the mounting means (14) isadapted for mounting adjacent a panel (61) of a housing of apparatus(62) to be tested in which the light emitting devices (5) are located onthe panel (61), the mounting means (14) positioning the respectivecollecting means (10) adjacent to the respective light emitting devices(5) on the panel (61) of the apparatus (62) to be tested.
 22. Apparatusas claimed in claim 1 wherein the apparatus further comprises a controlmeans (8,9,65) for controlling a supply of power to the light emittingdevices (5).
 23. A test fixture for testing electronic components andlight emitting devices connected to a printed circuit board (2), thetest fixture comprising: a base for receiving the printed circuit board,a plurality of light collecting means, one light collecting means beingprovided for each light emitting device for collecting light from thecorresponding light emitting device, an analyzing means for analyzinglight from the respective light collecting means, and a verifying meansfor verifying that each light emitting device is emitting light of thecorrect color, wherein the analyzing means comprises an image sensingpanel comprising a plurality of pixels arranged in a matrix of rows andcolumns, and the respective collecting means direct collected light ontothe image sensing panel at respective spaced apart locations so that thecollected light from the respective light emitting devices is incidenton corresponding pixels of the image sensing panel.
 24. A test fixtureas claimed in claim 23 wherein the mounting means (14) is mounted in thetest fixture (1) so that the mounting means (14) can be urged towardsthe printed circuit board (5) for bringing of the correspondingcollecting means into close proximity with the corresponding lightemitting devices (5) to be tested.